To facilitate the work for setting the diameter of a drum composed of individual length-measuring drum pieces.

This setting apparatus is provided with a 1st cam 13 for simultaneously driving length-measuring drum pieces 11 in radial direction, a 2nd cam 23 for simultaneously driving feeding drum pieces 21 in radial direction, magnets 41, 42 interlocking the 1st and the 2nd cams 13, 23 and a driving gear 31, for rotating the 2nd cam 23. When the 2nd cam 23 is rotated via the driving gear 31, the 1st cam 13 is driven to simultaneously shift the length-measuring drum pieces 11 and the feeding drum pieces 21.